Historically, transparent tubes containing a float or “bobbin” have been used as a means of measuring flow in gas and liquid systems. Visually observing the level of the bobbin alongside scaled markings on a plastic strip adjacent to the tube or printed on the walls of the tube itself, enables users to accurately gauge the flow of gas or liquid being applied to the system. Traditionally, such gauging devices have utilized an elongated illumination source positioned behind the flow tube and scale strip. While providing an extremely reliable means for measuring flow, this traditional method is difficult to read accurately and does not provide for optimal visualization when used in low light conditions, such as those found in today's operating rooms.
Lengthwise illumination of the flow tube along with illumination of a needle gauge has been used to assist the user in taking readings. For example, United States Patent Application Number 20080251003, assigned to Aviation Oxygen Systems, Inc., describes “[a]n illuminated gas flow tube comprises an in-line flow tube having a distal end and a proximal end. A gas inlet is co-axially secured to the distal end, and a gas outlet is co-axially secured to the proximal end. A specific gravity ball is located within the in-line flow tube, and moves within the flow tube as a function of gas entering the gas inlet. A phosphorescent or photoluminescent material is configured and arranged to at least partially lengthwise surround a radial exterior portion of the flow tube to illuminate the interior of the tube. An illuminated gas pressure gauge comprises an gas inlet, a pressure sensing element, a transparent cover, and a face that is encased by and seen through the transparent cover, where the face includes markings indicative of pressure. A needle is operatively connected to the pressure sensing element and seen through the transparent cover to provide a visual indication of pressure at the gas inlet, where the face is coated with an illuminating material that allows the gauge to be read in low light conditions.”
In addition, newer flow gauging devices, specifically those used in modern anesthesia machines, now use electronic flow measurement and display the data graphically on a video user interface. These newer systems have the advantage of providing digital outputs and enabling the user to directly input the flow data into the patient's records.
Although these new electronic devices provide accurate and visually appealing flow data, a need exists to provide a reliable flow tube device that works via a mechanical method in the event of electronic system failure. The user will also desire the mechanical flow tube as a “double check” of the digital data. In addition, the mechanical flow tube device needs to display the flow data in a manner that matches newer electronic displays and can be read optimally in low light conditions.